Why does it open my old project every time I create new file after reinstalling Blender?
I would guess you've had that project open, deliberately, since installing the new Blender? If so, you've probably pressed Ctrl+U, which saves the opened file as your start-up scene. You'll need to delete all objects and set it up as much as you can remember like the normal start-up scene, then press Ctrl+U, and say "yes" when it asks you if you want to "Save Start-up Scene."